Three-piece infrared single wavelength lens system

ABSTRACT

A three-piece infrared single wavelength lens system includes, in order from the object side to the image side: a stop, a first lens element with a positive refractive power, a second lens element with a positive refractive power, and a third lens element with a positive refractive power. The focal length of the first lens element is f1, the focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.5&lt;f1/f23&lt;1.0. When the above relation is satisfied, a wide field of view can be obtained and the resolution can be improved evidently.

BACKGROUND

Field of the Invention

The present invention relates to a lens system, and more particularly to a miniaturized three-piece infrared single wavelength lens system applicable to electronic products.

Description of the Prior Art

Nowadays digital imaging technology is constantly innovating and changing, in particular, digital carriers, such as, digital camera and mobile phone and so on, have become smaller in size, so CCD (Charge Coupled Device) or CMOS

(Complementary Metal Oxide Semiconductor) sensor is also required to be more compact. In addition to be used in the field of photography, in recent years, infrared focusing lens has also be used in infrared receiving and sensing field of the game machine, and in order to make the scope of game machine induction user more broader, wide-angle lens group has become the mainstream for receiving infrared wavelength at present.

The applicant has also put forward a number of lens groups related to infrared wavelength reception, such as the single focus wide-angle lens modules disclosed in TW Appl. Nos. 098100552, 098125378 and U.S. Pat. Nos. 8,031,413, 8,369,031, however, at present, the game machine is based on a more three-dimensional, real and immediate 3D game, the current or the applicant's previous lens groups are all 2D plane games, which cannot meet the 3D game focusing on the deep induction efficacy.

Special infrared receiving and induction lens groups for game machines are made of plastic for the pursuit of low cost, however, poor material transparency is one of the key factors that affect the depth detection accuracy of the game machine, and plastic lenses are easy to overheat or too cold in ambient temperature, so that the focal length of the lens group will be changed and cannot focus accurately. Therefore, the current infrared receiving and induction lens groups cannot meet the 3D game depth precise induction requirement.

The present invention mitigates and/or obviates the aforementioned disadvantages.

SUMMARY OF THE INVENTION

The present invention is aimed at providing a three-piece infrared single wavelength lens system with better image sensing function.

Therefore, a three-piece infrared single wavelength lens system in accordance with the present invention comprises, in order from an object side to an image side: a stop; a first lens element with a positive refractive power, having an object-side surface being convex near an optical axis and an image-side surface being convex near the optical axis, at least one of the object-side surface and the image-side surface of the first lens element being aspheric; a second lens element with a positive refractive power, having an object-side surface being concave near the optical axis and an image-side surface being convex near the optical axis, at least one of the object-side surface and the image-side surface of the second lens element being aspheric; and a third lens element with a positive refractive power having an object-side surface being convex near the optical axis and an image-side surface being concave near the optical axis, at least one of the object-side surface and the image-side surface of the third lens element being aspheric.

A focal length of the first lens element is f1, a focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.5<f1/f23<1.0, so that a wide field of view can be obtained and the resolution can be improved evidently.

Preferably, the focal length of the first lens element is f1, a focal length of the second lens element is f2, and they satisfy the relation: 0.05<f1/f2<0.45, so that the refractive power of the first lens element and the second lens element are more suitable, it will be favorable to obtain a wide field of view and avoid the excessive increase of aberration of the system.

Preferably, the focal length of the second lens element is f2, a focal length of the third lens element is f3, and they satisfy the relation: 0.5<f2/f3<2.6, so that the refractive power of the second lens element and the third lens element are more balanced, it will be favorable to correct the aberration of the system and reduce the sensitivity of the system.

Preferably, the focal length of the first lens element is f1, the focal length of the third lens element is f3, and they satisfy the relation: 0.05<f1/f3<0.7, so that the positive refractive power of the first lens element can be distributed effectively, so as to reduce the sensitivity of the three-piece infrared single wavelength lens system.

Preferably, a focal length of the first lens element and the second lens element combined is f12, the focal length of the third lens element is f3, and they satisfy the relation: 0.1<f12/f3<0.65, so that a wide field of view can be obtained and the resolution can be improved evidently.

Preferably, a radius of curvature of the image-side surface of the first lens element is R2, a radius of curvature of the object-side surface of the second lens element is R3, and they satisfy the relation: 25<R2/R3<270, which can reduce the spherical aberration and astigmatism of the three-piece infrared single wavelength lens system.

Preferably, the three-piece infrared single wavelength lens system has a maximum view angle FOV, and it satisfies the relation: 45<FOV<75, so that the three-piece infrared single wavelength lens system will have an appropriately large field of view.

Preferably, a central thickness of the first lens element along the optical axis is CT1, a distance along the optical axis between the first lens element and the second lens element is T12, and they satisfy the relation: 1.4<CT1/T12<2.4, which is favorable to the assembly of the lens group, improving the yield of production.

Preferably, the distance along the optical axis between the first lens element and the second lens element is T12, a central thickness of the second lens element along the optical axis is CT2, and they satisfy the relation: 0.5<T12/CT2<1.4, which is favorable to the formation and homogeneity of lenses and can increase the yield of assembly.

Preferably, the distance along the optical axis between the first lens element and the second lens element is T12, a distance along the optical axis between the second lens element and the third lens element is T23, and they satisfy the relation: 5.4<T12/T23<9.0, so that the distance between the lens elements is more suitable, it will be favorable to the assembly of the lenses, increasing the yield of finished products.

Preferably, an Abbe number of the first lens element is V1, an Abbe number of the second lens element is V2, and they satisfy the relation: 30<V1-V2<42, which can reduce the spherical aberration and astigmatism of the three-piece infrared single wavelength lens system effectively.

Preferably, the Abbe number of the first lens element is V1, an Abbe number of the third lens element is V3, and they satisfy the relation: 30<V1-V3<42, so that the chromatic aberration of the three-piece infrared single wavelength lens system can be modified effectively, improving the image quality.

Preferably, a f-number of the three-piece infrared single wavelength lens system is Fno, and it satisfies the relation: 1.2<Fno<1.8, so that the size of the stop of the three-piece infrared single wavelength lens system can be adjusted properly, making the three-piece infrared single wavelength lens system has a big stop.

The present invention will be presented in further details from the following descriptions with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiments in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a three-piece infrared single wavelength lens system in accordance with a first embodiment of the present invention;

FIG. 1B shows the longitudinal spherical aberration curve, the astigmatic field curve and the distortion curve of the first embodiment of the present invention;

FIG. 2A shows a three-piece infrared single wavelength lens system in accordance with a second embodiment of the present invention;

FIG. 2B shows the longitudinal spherical aberration curve, the astigmatic field curve and the distortion curve of the second embodiment of the present invention;

FIG. 3A shows a three-piece infrared single wavelength lens system in accordance with a third embodiment of the present invention;

FIG. 3B shows the longitudinal spherical aberration curve, the astigmatic field curve and the distortion curve of the third embodiment of the present invention;

FIG. 4A shows a three-piece infrared single wavelength lens system in accordance with a fourth embodiment of the present invention; and

FIG. 4B shows the longitudinal spherical aberration curve, the astigmatic field curve and the distortion curve of the fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1A and 1B, FIG. 1A shows a three-piece infrared single wavelength lens system in accordance with a first embodiment of the present invention, and FIG. 1B shows, in order from left to right, the longitudinal spherical aberration curves, the astigmatic field curves, and the distortion curve of the first embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the first embodiment of the present invention comprises a stop 100 and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element 110, a second lens element 120, a third lens element 130, an IR cut filter 170, and an image plane 180, wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop 100 is disposed between an image-side surface 112 of the first lens element 110 and an object to be imaged.

The first lens element 110 with a positive refractive power has an object-side surface 111 being convex near an optical axis 190 and the image-side surface 112 being convex near the optical axis 190, the object-side surface 111 and the image-side surface 112 are aspheric, and the first lens element 110 is made of plastic material.

The second lens element 120 with a positive refractive power has an object-side surface 121 being concave near the optical axis 190 and an image-side surface 122 being convex near the optical axis 190, the object-side surface 121 and the image-side surface 122 are aspheric, and the second lens element 120 is made of plastic material.

The third lens element 130 with a positive refractive power has an object-side surface 131 being convex near the optical axis 190 and an image-side surface 132 being concave near the optical axis 190, the object-side surface 131 and the image-side surface 132 are aspheric, and the third lens element 130 is made of plastic material.

The IR cut filter 170 made of glass is located between the third lens element 130 and the image plane 180 and has no influence on the focal length of the three-piece infrared single wavelength lens system.

The equation for the aspheric surface profiles of the respective lens elements of the first embodiment is expressed as follows:

wherein:

$z = {\frac{{ch}^{2}}{1 + \left\lbrack {1 - {\left( {k + 1} \right)c^{2}h^{2}}} \right\rbrack^{0.5}} + {Ah}^{4} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + {Eh}^{12} + {Gh}^{14} + \ldots}$

z represents the value of a reference position with respect to a vertex of the surface of a lens and a position with a height h along the optical axis 190;

c represents a paraxial curvature equal to 1/R (R: a paraxial radius of curvature);

h represents a vertical distance from the point on the curve of the aspheric surface to the optical axis 190;

k represents the conic constant;

A, B, C, D, E, G, . . . : represent the high-order aspheric coefficients.

In the first embodiment of the present three-piece infrared single wavelength lens system, a focal length of the three-piece infrared single wavelength lens system is f, a f-number of the three-piece infrared single wavelength lens system is Fno, the three-piece infrared single wavelength lens system has a maximum view angle (field of view) FOV, and they satisfy the relations: f=1.192 mm; Fno=1.4; and FOV=60 degrees.

In the first embodiment of the present three-piece infrared single wavelength lens system, a focal length of the first lens element 110 is f1, a focal length of the second lens element 120 and the third lens element 130 combined is f23, and they satisfy the relation: f1/f23=0.64636.

In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the first lens element 110 is f1, a focal length of the second lens element 120 is f2, and they satisfy the relation: f1/f2=0.22985.

In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the second lens element 120 is f2, a focal length of the third lens element 130 is f3, and they satisfy the relation: f2/f3=1.39174.

In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the first lens element 110 is f1, the focal length of the third lens element 130 is f3, and they satisfy the relation: f1/f3=0.31990.

In the first embodiment of the present three-piece infrared single wavelength lens system, a focal length of the first lens element 110 and the second lens element 120 combined is f12, the focal length of the third lens element 130 is f3, and they satisfy the relation: f12/f3=0.32798.

In the first embodiment of the present three-piece infrared single wavelength lens system, a radius of curvature of the image-side surface 112 of the first lens element 110 is R2, a radius of curvature of the object-side surface 121 of the second lens element 120 is R3, and they satisfy the relation: R2/R3=261.90368.

In the first embodiment of the present three-piece infrared single wavelength lens system, a central thickness of the first lens element 110 along the optical axis 190 is CT1, a distance along the optical axis 190 between the first lens element 110 and the second lens element 120 is T12, and they satisfy the relation: CT1/T12=1.85473.

In the first embodiment of the present three-piece infrared single wavelength lens system, the distance along the optical axis 190 between the first lens element 110 and the second lens element 120 is T12, a central thickness of the second lens element 120 along the optical axis 190 is CT2, and they satisfy the relation: T12/CT2=0.97384.

In the first embodiment of the present three-piece infrared single wavelength lens system, the distance along the optical axis 190 between the first lens element 110 and the second lens element 120 is T12, a distance along the optical axis 190 between the second lens element 120 and the third lens element 130 is T23, and they satisfy the relation: T12/T23=7.159.

In the first embodiment of the present three-piece infrared single wavelength lens system, an Abbe number of the first lens element 110 is V1, an Abbe number of the second lens element 120 is V2, and they satisfy the relation: V1-V2=34.5.

In the first embodiment of the present three-piece infrared single wavelength lens system, the Abbe number of the first lens element 110 is V1, an Abbe number of the third lens element 130 is V3, and they satisfy the relation: V1-V3=34.5.

The detailed optical data of the first embodiment is shown in table 1, and the aspheric surface data is shown in table 2.

TABLE 1 Embodiment 1 f(focal length) = 1.192 mm, Fno = 1.4, FOV = 60 deg. Curvature surface Radius Thickness Material Index Abbe # Focal length 0 object infinity 500.000 1 infinity 0.002 2 stop infinity −0.002 3 Lens 1 0.866 (ASP) 0.398 plastic 1.544 56.000 1.610 4 −107.896 (ASP) 0.215 5 Lens 2 −0.412 (ASP) 0.221 plastic 1.651 21.500 7.005 6 −0.454 (ASP) 0.030 7 Lens 3 0.658 (ASP) 0.256 plastic 1.651 21.500 5.034 8 0.707 (ASP) 0.379 9 IR-filter infinity 0.210 glass 1.517 64.167 — 10 infinity 0.131 11 Image infinity 0.000 plane

TABLE 2 Aspheric Coefficients surface 3 4 5 K: 1.6561E−01 9.0001E+01 −5.0677E−01 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −1.7783E−01 −3.8297E−01 2.8597E+00 C: 2.2848E+00 7.7170E+00 −5.9554E+00 D: −5.8170E+01 −1.3481E+02 −6.6323E+01 E: 5.3783E+02 1.0727E+03 1.1671E+03 F: −2.3081E+03 −3.8622E+03 −4.7624E+03 G 3.4798E+03 4.9505E+03 6.3678E+03 H 0.0000E+00 0.0000E+00 0.0000E+00 surface 6 7 8 K: −1.5487E+00 −1.1929E+01 −6.9879E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −4.3135E−01 2.0091E+00 −5.2294E−01 C: 5.6008E+00 −2.1131E+01 1.5078E+00 D: −5.8963E+01 1.1419E+02 −1.1792E+01 E: 3.4446E+02 −3.9602E+02 3.2929E+01 F: −7.4388E+02 7.4075E+02 −5.7999E+01 G 5.0956E+02 −6.2921E+02 4.4847E+01 H 0.0000E+00 0.0000E+00 0.0000E+00

The units of the radius of curvature, the thickness and the focal length in table 1 are expressed in mm, the surface numbers 0-11 represent the surfaces sequentially arranged from the object-side to the image-side along the optical axis. In table 2, k represents the conic coefficient of the equation of the aspheric surface profiles, and A, B, C, D, E, F, G, H . . . : represent the high-order aspheric coefficients. The tables presented below for each embodiment are the corresponding schematic parameter and aberration curves, and the definitions of the tables are the same as Table 1 and Table 2 of the first embodiment. Therefore, an explanation in this regard will not be provided again.

Referring to FIGS. 2A and 2B, FIG. 2A shows a three-piece infrared single wavelength lens system in accordance with a second embodiment of the present invention, and FIG. 2B shows, in order from left to right, the longitudinal spherical aberration curves, the astigmatic field curves, and the distortion curve of the second embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the second embodiment of the present invention comprises a stop 200 and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element 210, a second lens element 220, a third lens element 230, an IR cut filter 270, and an image plane 280, wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop 200 is disposed between an image-side surface 212 of the first lens element 210 and an object to be imaged.

The first lens element 210 with a positive refractive power has an object-side surface 211 being convex near an optical axis 290 and the image-side surface 212 being convex near the optical axis 290, the object-side surface 211 and the image-side surface 212 are aspheric, and the first lens element 210 is made of plastic material.

The second lens element 220 with a positive refractive power has an object-side surface 221 being concave near the optical axis 290 and an image-side surface 222 being convex near the optical axis 290, the object-side surface 221 and the image-side surface 222 are aspheric, and the second lens element 220 is made of plastic material.

The third lens element 230 with a positive refractive power has an object-side surface 231 being convex near the optical axis 290 and an image-side surface 232 being concave near the optical axis 290, the object-side surface 231 and the image-side surface 232 are aspheric, and the third lens element 230 is made of plastic material.

The IR cut filter 270 made of glass is located between the third lens element 230 and the image plane 280 and has no influence on the focal length of the three-piece infrared single wavelength lens system.

The detailed optical data of the second embodiment is shown in table 3, and the aspheric surface data is shown in table 4.

TABLE 3 Embodiment 2 f(focal length) = 1.264 mm, Fno = 1.4, FOV = 55 deg. Curvature surface Radius Thickness Material Index Abbe # Focal length 0 object infinity 500.000 1 infinity 0.003 2 stop infinity −0.003 3 Lens 1 0.956 (ASP) 0.479 plastic 1.544 56.000 1.760 4 −56.134 (ASP) 0.258 5 Lens 2 −0.453 (ASP) 0.221 plastic 1.651 21.500 9.111 6 −0.499 (ASP) 0.030 7 Lens 3 0.669 (ASP) 0.274 plastic 1.651 21.500 4.227 8 0.752 (ASP) 0.367 9 IR-filter infinity 0.210 glass 1.517 64.167 — 10 infinity 0.144 11 Image infinity 0.000 plane

TABLE 4 Aspheric Coefficients surface 3 4 5 K: 1.4591E−01 8.6453E+03 −5.0418E−01 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −1.4983E−01 −2.5141E−01 2.1650E+00 C: 1.4038E+00 4.8007E+00 −3.7831E+00 D: −2.9628E+01 −6.9229E+01 −3.4353E+01 E: 2.2943E+02 4.5491E+02 4.9418E+02 F: −8.0646E+02 −1.3541E+03 −1.6700E+03 G 1.0122E+03 1.4330E+03 1.8433E+03 H 0.0000E+00 0.0000E+00 0.0000E+00 surface 6 7 8 K: −1.4998E+00 −1.0282E+01 −5.4983E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −3.2878E−01 1.8526E+00 −8.3680E−02 C: 3.5347E+00 −1.3143E+01 1.1134E+00 D: −3.0133E+01 5.8273E+01 −6.4602E+00 E: 1.4609E+02 −1.6768E+02 1.3145E+01 F: −2.6120E+02 2.6112E+02 −2.0481E+01 G 1.4485E+02 −1.7938E+02 1.5542E+01 H 0.0000E+00 0.0000E+00 0.0000E+00

In the second embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the second embodiment, so an explanation in this regard will not be provided again.

Moreover, these parameters can be calculated from Table 3 and Table 4 as the following values and satisfy the following conditions:

Embodiment 2 f 1.264 f12/f3 0.43356 Fno 1.4 R2/R3 123.96486 FOV 55 CT1/T12 1.85478 f1/f2 0.19314 T12/CT2 1.16877 f2/f3 2.15539 T12/T23 8.60333 f1/f3 0.41629 V1 − V2 34.5 f1/f23 0.71360 V1 − V3 34.5

Referring to FIGS. 3A and 3B, FIG. 3A shows a three-piece infrared single wavelength lens system in accordance with a third embodiment of the present invention, and FIG. 3B shows, in order from left to right, the longitudinal spherical aberration curves, the astigmatic field curves, and the distortion curve of the third embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the third embodiment of the present invention comprises a stop 300 and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element 310, a second lens element 320, a third lens element 330, an IR cut filter 370, and an image plane 380, wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop 300 is disposed between an image-side surface 312 of the first lens element 310 and an object to be imaged.

The first lens element 310 with a positive refractive power has an object-side surface 311 being convex near an optical axis 390 and the image-side surface 312 being convex near the optical axis 390, the object-side surface 311 and the image-side surface 312 are aspheric, and the first lens element 310 is made of plastic material.

The second lens element 320 with a positive refractive power has an object-side surface 321 being concave near the optical axis 390 and an image-side surface 322 being convex near the optical axis 390, the object-side surface 321 and the image-side surface 322 are aspheric, and the second lens element 320 is made of plastic material.

The third lens element 330 with a positive refractive power has an object-side surface 331 being convex near the optical axis 390 and an image-side surface 332 being concave near the optical axis 390, the object-side surface 331 and the image-side surface 332 are aspheric, and the third lens element 330 is made of plastic material.

The IR cut filter 370 made of glass is located between the third lens element 330 and the image plane 380 and has no influence on the focal length of the three-piece infrared single wavelength lens system.

The detailed optical data of the third embodiment is shown in table 5, and the aspheric surface data is shown in table 6.

TABLE 5 Embodiment 3 f(focal length) = 1.076 mm, Fno = 1.6, FOV = 65 deg. Curvature surface Radius Thickness Material Index Abbe # Focal length 0 object infinity 500.000 1 infinity −0.054 2 stop infinity 0.054 3 Lens 1 0.876 (ASP) 0.358 plastic 1.544 56.000 1.602 4 −37.188 (ASP) 0.211 5 Lens 2 −0.412 (ASP) 0.213 plastic 1.651 21.500 7.268 6 −0.453 (ASP) 0.030 7 Lens 3 0.626 (ASP) 0.254 plastic 1.651 21.500 3.216 8 0.764 (ASP) 0.333 9 IR-filter infinity 0.210 glass 1.517 64.167 — 10 infinity 0.131 11 Image infinity 0.000 plane

TABLE 6 Aspheric Coefficients surface 3 4 5 K: 1.1143E−01 4.5584E+03 −5.0524E−01 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −2.6472E−01 −4.3381E−01 3.0370E+00 C: 2.4231E+00 1.0284E+01 −1.0318E+01 D: −3.2150E+01 −1.4021E+02 −1.4086E+01 E: 1.7801E+02 9.7852E+02 8.8790E+02 F: −6.4089E+02 −3.3473E+03 −4.0655E+03 G 8.4568E+02 4.1659E+03 5.7099E+03 H 0.0000E+00 0.0000E+00 0.0000E+00 surface 6 7 8 K: −1.4714E+00 −1.2397E+01 −6.4401E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −4.9828E−01 2.6913E+00 −4.5859E−01 C: 6.5987E+00 −2.3621E+01 5.1313E+00 D: −7.6651E+01 1.2891E+02 −3.6777E+01 E: 4.6447E+02 −4.6825E+02 1.1797E+02 F: −1.0766E+03 9.5965E+02 −1.9549E+02 G 8.5055E+02 −8.6698E+02 1.2566E+02 H 0.0000E+00 0.0000E+00 0.0000E+00

In the third embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the third embodiment, so an explanation in this regard will not be provided again.

Moreover, these parameters can be calculated from Table 5 and Table 6 as the following values and satisfy the following conditions:

Embodiment 3 f 1.076 f12/f3 0.50896 Fno 1.6 R2/R3 90.34390 FOV 65 CT1/T12 1.69914 f1/f2 0.22035 T12/CT2 0.98882 f2/f3 2.26020 T12/T23 7.01767 f1/f3 0.49804 V1 − V2 34.5 f1/f23 0.84401 V1 − V3 34.5

Referring to FIGS. 4A and 4B, FIG. 4A shows a three-piece infrared single wavelength lens system in accordance with a fourth embodiment of the present invention, and FIG. 4B shows, in order from left to right, the longitudinal spherical aberration curves, the astigmatic field curves, and the distortion curve of the fourth embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the fourth embodiment of the present invention comprises a stop 400 and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element 410, a second lens element 420, a third lens element 430, an IR cut filter 470, and an image plane 480, wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop 400 is disposed between an image-side surface 412 of the first lens element 410 and an object to be imaged.

The first lens element 410 with a positive refractive power has an object-side surface 411 being convex near an optical axis 490 and the image-side surface 412 being convex near the optical axis 490, the object-side surface 411 and the image-side surface 412 are aspheric, and the first lens element 410 is made of plastic material.

The second lens element 420 with a positive refractive power has an object-side surface 421 being concave near the optical axis 490 and an image-side surface 422 being convex near the optical axis 490, the object-side surface 421 and the image-side surface 422 are aspheric, and the second lens element 420 is made of plastic material.

The third lens element 430 with a positive refractive power has an object-side surface 431 being convex near the optical axis 490 and an image-side surface 432 being concave near the optical axis 490, the object-side surface 431 and the image-side surface 432 are aspheric, and the third lens element 430 is made of plastic material.

The IR cut filter 470 made of glass is located between the third lens element 430 and the image plane 480 and has no influence on the focal length of the three-piece infrared single wavelength lens system.

The detailed optical data of the fourth embodiment is shown in table 7, and the aspheric surface data is shown in table 8.

TABLE 7 Embodiment 4 f(focal length) = 1.11 mm, Fno = 1.4, FOV = 64 deg. Curvature surface Radius Thickness Material Index Abbe # Focal length 0 object infinity 500.000 1 infinity 0.000 2 stop infinity 0.000 3 Lens 1 0.848 (ASP) 0.364 plastic 1.544 56.000 1.508 4 −13.555 (ASP) 0.173 5 Lens 2 −0.416 (ASP) 0.234 plastic 1.635 23.900 5.081 6 −0.445 (ASP) 0.030 7 Lens 3 0.612 (ASP) 0.236 plastic 1.635 23.900 6.070 8 0.625 (ASP) 0.358 9 IR-filter infinity 0.210 glass 1.517 64.167 — 10 infinity 0.131 11 Image infinity 0.000 plane

TABLE 8 Aspheric coefficients surface 3 4 5 K: −6.8165E−02 −6.6204E+01 −5.5086E−01 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −9.2855E−02 −3.9781E−01 2.8075E+00 C: −1.7300E+00 −9.5082E−01 −1.4380E+01 D: −1.1434E+01 7.3878E+00 1.3482E+02 E: 3.1050E+02 2.2340E+00 −3.5346E+02 F: −2.3349E+03 −1.6160E+02 3.2516E+02 G 5.0324E+03 3.4273E+02 −1.3212E+01 H 0.0000E+00 0.0000E+00 0.0000E+00 surface 6 7 8 K: −1.6842E+00 −1.0036E+01 −6.3872E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −4.2370E−01 2.1256E+00 −2.1000E−01 C: 2.6819E+00 −2.0101E+01 5.4441E−01 D: 8.1475E+00 1.1789E+02 −5.4072E+00 E: −8.0008E+01 −4.9289E+02 −5.1579E+00 F: 4.9479E+02 1.1501E+03 3.0434E+01 G −8.8479E+02 −1.2123E+03 −2.9698E+01 H 0.0000E+00 0.0000E+00 0.0000E+00

In the fourth embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the fourth embodiment, so an explanation in this regard will not be provided again.

Moreover, these parameters can be calculated from Table 7 and Table 8 as the following values and satisfy the following conditions:

Embodiment 4 f 1.11 f12/f3 0.24379 Fno 1.4 R2/R3 32.60571 FOV 64 CT1/T12 2.10076 f1/f2 0.29673 T12/CT2 0.74124 f2/f3 0.83702 T12/T23 5.77300 f1/f3 0.24837 V1 − V2 32.1 f1/f23 0.63936 V1 − V3 32.1

In the present three-piece infrared single wavelength lens system, the lens elements can be made of plastic or glass. If the lens elements are made of plastic, the cost will be effectively reduced. If the lens elements are made of glass, there is more freedom in distributing the refractive power of the three-piece infrared single wavelength lens system. Plastic lens elements can have aspheric surfaces, which allow more design parameter freedom (than spherical surfaces), so as to reduce the aberration and the number of the lens elements, as well as the total track length of the three-piece infrared single wavelength lens system.

In the present three-piece infrared single wavelength lens system, if the object-side or the image-side surface of the lens elements with refractive power is convex and the location of the convex surface is not defined, the object-side or the image-side surface of the lens elements near the optical axis is convex. If the object-side or the image-side surface of the lens elements is concave and the location of the concave surface is not defined, the object-side or the image-side surface of the lens elements near the optical axis is concave.

The three-piece infrared single wavelength lens system of the present invention can be used in focusing optical systems and can obtain better image quality. The three-piece infrared single wavelength lens system of the present invention can also be used in electronic imaging systems, such as, 3D image capturing, digital camera, mobile device, digital flat panel or vehicle camera.

While we have shown and described various embodiments in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention. 

1. A three-piece infrared single wavelength lens system, in order from an object side to an image side, comprising: a stop; a first lens element with a positive refractive power, having an object-side surface being convex near an optical axis and an image-side surface being convex near the optical axis, at least one of the object-side surface and the image-side surface of the first lens element being aspheric; a second lens element with a positive refractive power, having an object-side surface being concave near the optical axis and an image-side surface being convex near the optical axis, at least one of the object-side surface and the image-side surface of the second lens element being aspheric; and a third lens element with a positive refractive power, having an object-side surface being convex near the optical axis an image-side surface being concave near the optical axis, at least one of the object-side surface and the image-side surface of the third lens element being aspheric; wherein a focal length of the first lens element is f1, a focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.5<f1/f23<1.0.
 2. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein the focal length of the first lens element is f1, a focal length of the second lens element is f2, and they satisfy the relation: 0.05<f1/f2<0.45.
 3. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein a focal length of the second lens element is f2, a focal length of the third lens element is f3, and they satisfy the relation: 0.5<f2/f3<2.6.
 4. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein the focal length of the first lens element is f1, a focal length of the third lens element is f3, and they satisfy the relation: 0.05<f1/f3<0.7.
 5. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein a focal length of the first lens element and the second lens element combined is f12, a focal length of the third lens element is f3, and they satisfy the relation: 0.1<f12/f3<0.65.
 6. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein a radius of curvature of the image-side surface of the first lens element is R2, a radius of curvature of the object-side surface of the second lens element is R3, and they satisfy the relation: 25<R2/R3<270.
 7. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein the three-piece infrared single wavelength lens system has a maximum view angle FOV, and it satisfies the relation: 45<FOV<75.
 8. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein a central thickness of the first lens element along the optical axis is CT1, a distance along the optical axis between the first lens element and the second lens element is T12, and they satisfy the relation: 1.4<CT1/T12<2.4.
 9. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein a distance along the optical axis between the first lens element and the second lens element is T12, a central thickness of the second lens element along the optical axis is CT2, and they satisfy the relation: 0.5<T12/CT2<1.4.
 10. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein a distance along the optical axis between the first lens element and the second lens element is T12, a distance along the optical axis between the second lens element and the third lens element is T23, and they satisfy the relation: 5.4<T12/T23<9.0.
 11. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein an Abbe number of the first lens element is V1, an Abbe number of the second lens element is V2, and they satisfy the relation: 30<V1-V2<42.
 12. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein an Abbe number of the first lens element is V1, an Abbe number of the third lens element is V3, and they satisfy the relation: 30<V1-V3<42.
 13. The three-piece infrared single wavelength lens system as claimed in claim 1, wherein a f-number of the three-piece infrared single wavelength lens system is Fno, and it satisfies the relation: 1.2<Fno<1.8. 